The massive beige-and-white building on Dakhdaev Street was probably the safest place the FBI could find to work this week in the southern Russian city of Makhachkala, where bombings and counterterrorism raids are a routine part of life for the locals. That building is the regional headquarters of the FSB, the state security service that replaced the KGB after the fall of the Soviet Union, and it is fenced off with tall iron bars, blocked from the street by concrete slabs and guarded day and night by surly special-forces troops in full combat gear. So when the American investigators arrived in the Russian region of Dagestan on Tuesday to interview the parents of the Tsarnaev brothers, the prime suspects in the bombing of the Boston Marathon last week, the questioning took place inside that building. In light of recent tensions between the U.S. and Russia, the FSB’s hospitality seems remarkable, and it shows how much the Boston bombings have changed the tone between the secret services.

On Wednesday morning, an official at the U.S. embassy in Moscow told TIME that the FBI “is receiving cooperation from the Russian government in its investigation of the Boston Marathon bombing.” Speaking on customary condition of anonymity, the official added: “A group from the U.S. embassy in Moscow traveled to Dagestan yesterday [April 23] as part of this cooperation with the Russian government to interview the parents [of the Tsarnaev brothers].”

That day, Zubeidat Tsarnaeva, the mother of the suspected Boston bombers, was questioned for around eight hours by both the FSB and FBI and only allowed to go home around midnight, according to Heda Saratova, a local rights activist who has been working closely with the family. “The atmosphere was very cordial,” Saratova told TIME after speaking with Tsarnaeva. “But she was exhausted afterwards, as if in a trance.” For reasons of health, Anzor Tsarnaev, the father of the suspected bombers, stayed home on Tuesday, but the following day both of the parents were questioned for another eight hours. “The FBI and FSB were both there. They were working together,” said Zaurbek Sadakhanov, a lawyer who has been consulting the family and spoke to them after the second day of questioning.

Even a few months ago, it would have been hard to imagine the FBI and FSB helping each other so openly. The political atmosphere between their two countries has recently become so combative that it has poisoned relations between the special services. In January, Moscow even pulled out of an 11-year-old agreement between the U.S. and Russia to cooperate on issues of law enforcement and security. Some channels did remain open, as became clear after the Boston Marathon bombings, but their usefulness was apparently stilted by a lack of follow-through.

On April 19, the FBI revealed that it had received information from a “foreign government” that Tamerlan Tsarnaev, the prime suspect in the bombings who was killed in a shootout with police on Friday, had links to religious extremists. (On April 24, Republican Senator Saxby Chambliss claimed the Russians had approached the U.S. twice in 2011 regarding Tsarnaev.) TIME’s sources in the security services in Dagestan confirmed that this information came from the FSB. Local agents had flagged Tsarnaev as a potential extremist in 2011 after he attended services at a mosque in Makhachkala where suspected terrorists have been known to congregate.

The FBI looked into the claims but found no signs that Tsarnaev was linked to terrorism. “The FBI requested but did not receive more specific or additional information from the foreign government,” the agency said in its statement. TIME’s security source in Makhachkala, who specializes in religious radicalism in Dagestan, said he was not senior enough to know the details of the back-and-forth of these transnational communiqués, which are usually conducted through the FSB’s federal headquarters. “There was a request passed along for more information,” he said. But he was not aware of a similar request being sent back from the FBI to the FSB. “That would have been through Moscow, so I don’t know.” The fact that such information did not seem to reach agents working on the ground is itself an indication of the overly bureaucratized and slow nature of this process.

Andrei Soldatov, an expert and author on the Russian security services in Moscow, said the FSB does not seem to have opened a two-way line of communication with the FBI on the Tsarnaev case. “In the case of Tsarnaev, that seems to have been a request. It was not an invitation. It said, Hey, I want to get information from you,” says Soldatov. Its failure to lead to more robust cooperation is perhaps a sign of the times. Several scandals, as well as a gradual erosion of trust, have broken many of the links the FSB and FBI maintained a decade ago.

The good old days of that relationship date back to 2003, when the agencies worked together on a sting operation to capture a suspected arms dealer named Hemant Lakhani, a British citizen of Indian origin. A group of Russian agents, posing as disgruntled military officers, provided Lakhani with a set of surface-to-air missiles, which he then attempted to sell to a group of FBI agents pretending to be Somali terrorists. Before handing the missiles over to Lakhani, the Russians had disarmed them, and when Lakhani attempted to sell these Russian duds to undercover FBI agents, he was arrested and later convicted for attempting to provide material support to terrorists. The effort was trumpeted by U.S. officials as an “incredible triumph” in the war on terror.